Finland
August 24, 2009
The doctoral dissertation of MTT scientist Pirkko Laitinen is the first study to show a connection between glyphosate transport in plants and residues detected in soil. Glyphosate is one of the most widely used herbicides in the world. In Finland, it accounted for about 66% of all herbicide sales in 2007.
“The study indicated that glyphosate transport to plant roots involves a significant amount – more than 12% of the volume used. Transport within the plant must be taken into account in evaluating the environmental risks of glyphosate,” Pirkko Laitinen says.
Glyphosate does not decompose in plants. From the roots, the substance is released into soil, where microbes may decompose it, or it may bind to soil particles and leach further with water. Transport through the plant deep into the soil is a rapid process and can occur even under dry conditions.
Glyphosate may accumulate in a field
Laitinen’s study focused on the behaviour of glyphosate in arable land and how it depends on the soil phosphorus status of the field.
Glyphosate is an organic phosphorus compound, and as such it competes with soil phosphorus in binding sites. The research findings show that the higher the soil phosphorus level is, the weaker the binding of the glyphosate and consequently the higher the risk of leaching. The soil phosphorus level also affects glyphosate decomposition, as microbes decompose free glyphosate better than bound glyphosate. The accumulation and leaching risk for glyphosate may be estimated on the basis of the soil phosphorus level of the field.
“In Finland, the level of fertility phosphorus in fields is studied at regular intervals, so we have an extensive dataset available for risk assessment both regionally and at the farm and field level. The fertility phosphorus status could be a useful and economic tool for this evaluation,” Laitinen says.
“Glyphosate decomposes slowly in low-phosphorus soil. Repeated use of the substance without intermediate ploughin may lead to the glyphosate accumulating in the surface soil layer. Decomposition is slow after the autumn treatment, and the choice of tillage method influences whether the herbicide is leached into runoff or drainage water. Autumn treatment should be critically considered and limited, at least in certain areas,” Laitinen says.
Public examination of the doctoral dissertation of Pirkko Laitinen, ‘Fate of the organophosphate herbicide glyphosate in arable soils and its relationship to soil phosphorus status’ will take place at the University of Kuopio on 4 September 2009 at 12.00. Professor Markku Yli-Halla of the University of Helsinki will be the Opponent, and Docent Helvi Heinonen-Tanski of the University of Kuopio will serve as the Custos.
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